A. Field of the Invention
The present invention relates to devices for coupling together a pair of optical devices, such as a night-vision device to a telescopic sight mounted on a rifle. More particularly, the invention relates to a versatile clamping device for releasably and coaxially coupling an auxiliary optical device such as an infrared viewer, image intensifier, or other such night vision device used to enhance viewability of objects in dark environments, to a riflescope of the type useful primarily for daylight conditions, thus adapting the riflescope for nighttime use.
B. Description of Background Art.
A typical riflescope of the type used by hunters, law enforcement personal, and members of the military, comprises essentially a Galilean telescope which is provided with an internal sighting reticle. Most riflescopes have a longitudinally elongated, main tube, a short, front tubular objective lens assembly of a larger diameter joined to the main tube by a tapered frusto-conically-shaped front transition section, and a short, rear tubular eye-piece or ocular section holding an eyepiece, lens assembly, the rear tubular section being of a diameter intermediate that of the objective end piece and main tube, and joined to the latter by a rear tapered transition section.
A riflescope includes a mounting system for attaching it to a rifle, such as a mounting base which protrudes downwardly from the main tubular section of the riflescope and is adapted to be attached to a rifle mount that protrudes upwardly from the barrel of a rifle. The riflescope mount and rifle mount are so constructed as to enable the riflescope to be securely attached to the rifle, with the optical axis maintained substantially parallel to the bore axis of the rifle, using an elongated interlocking dove-tailed rail and channel, for example.
As can be readily understood, the function of a riflescope is to provide a magnified image of a distant target, to thereby facilitate aligning the trajectory of a bullet fired from the rifle with an intended location on a target. Thus, a riflescope is provided with some sort of visual indicator which is superimposed on a distant target and viewable through the eyepiece. Typically, the visual indicator is a reticle which has two or more perpendicular cross-hairs that intersect in the center of the field of view of the riflescope. Ideally, the intersection point of the reticle cross hairs on a target at a particular distance or range coincides with the impact point of a bullet fired from a rifle to which the riflescope is attached. However, since the trajectory of a bullet is a parabolic curve, rather than a straight line, the bullet impact point can be made to coincide precisely with the cross-hair intersection point on a distant target only at a specific range, e.g., 100 or 200 yards.
As a practical matter, if the ratio of muzzle velocity to weight of the fired bullet is sufficiently high, a bullet has a relatively flat trajectory, so that angular height deviations between the bullet impact point and the cross-hair intersection on a target will be tolerably small for reasonably large variations in range.
To enable alignment of the cross-hair intersection of a riflescope with the impact point of a rifle on which the riflescope is mounted, the riflescope contains a mechanism for aligning a line of sight defined by the eye and cross-hair intersection relative to the bore axis of the rifle. An alignment procedure, called boresighting, is generally accomplished by using a riflescope alignment adjustment mechanism which includes a pair of perpendicularly arranged, knurled thumb knobs which are mechanically coupled to horizontal and vertical cross-hairs. These include a first, elevation adjustment thumb knob which has a vertically disposed axis that protrudes upwardly from the upper surface of the central tubular section of the riflescope, at a location between the front and rear ends of the riflescope. The elevation thumb knob is rotatable in a horizontal plane in a clockwise or counterclockwise sense to raise or lower a horizontal cross-hair axis relative to the bore of the rifle.
Similarly, a typical riflescope includes a second, windage adjustment thumb knob which has a horizontally disposed axis that protrudes horizontally outwards from a side, e.g., right side, of the central tubular section of the riflescope, in transverse alignment with the elevation adjustment thumb knob. The windage adjustment thumb knob is rotatable in a vertical plane in clockwise and counterclockwise senses to move a vertical cross-hair aim point left or right relative to the bore of the rifle.
A customary method of boresighting a riflescope mounted on a rifle involves the steps of adjusting the elevation and windage thumb knobs to nominal values, firing the rifle at a target, noting the impact point of the bullet, re-adjusting the elevation and windage knobs to bring the aim point of the riflescope into closer coincidence with the bullet impact point on the target, firing the rifle again, and repeating the foregoing steps as many times as necessary to achieve a desired proximity between cross-hair aim point and bullet impact point.
When a rifle is to be fired at a target which differs substantially in range from the sight-in range used to boresight the riflescope to the rifle, the elevation angle of the cross-hairs may be raised or lowered to raise or lower the trajectory of the bullet a predetermined amount relative to the cross-hair aiming point, by turning the elevation knob in angular increments indicated by alignment of a particular one of a series of numbered fiduciary marks on the elevation knob with an index marker fixed to the riflescope tube. Similarly, in the presence of transverse cross winds, the windage adjustment thumb knob may be used to deviate the cross-hair aim point toward the direction of the wind, thus ensuring that the vector sum of trajectory of a bullet from the muzzle of the rifle, and the transverse deviation of the trajectory caused by wind result in an impact point close to a desired impact point on a target.
It should be noted that the angular adjustments of elevation and windage both for boresighting and adjusting to varied range and wind conditions, are quite critical. Thus, a deviation of only 0.095 degrees results in a one-foot deviation of a bullet impact point at 200 yards. Accordingly, it is important than the optical axis of the riflescope be maintained in a very rigid, stable, orientation relative to the bore of a rifle on which it is mounted.
Magnification of a target image using a typical riflescope substantially increases the range over which an average shooter can accurately fire on a target, as compared to the shooters use of mechanical sights which do not employ magnifying lenses, i.e., “iron sights.” However, the use of conventional telescopic riflescopes under low-light level conditions, e.g., at dusk or dawn, can be problematic for the following reasons.
Although a riflescope can in principle utilize any combination of magnifying power and objective lens size, practical considerations such as size and weight place limits on the foregoing parameters. Thus, a typical riflescope utilizes a 42 mm diameter objective lens, and has a magnification ratio of 10× and is thus designated 10×42. Now, the light gathering power of a telescopic sight or similar optical instrument is directly proportional to the area of the objective lens, and is inversely proportional to the magnification factor of the sight. Also, as a rough rule of thumb, it has been determined that a 7×50 telescope, such as the dual telescopes of 7×50 binoculars, provides an image brightness approximating that of an image viewed directly by the eye. Thus, the brightness of an image formed on the eye by a 10×42 riflescope, a riflescope having a smaller, 42 mm objective lens and a higher, 10× magnification factor, is substantially less than the brightness of an image formed on the eye using iron sights.
Also, there are a variety of situations in which it is desirable to be able to fire a rifle on a target in lighting conditions which would be impractical even using iron sights, i.e., at night. For such applications, a special type of riflescope called a “snooperscope” was developed many years ago. The original snooperscope employed an infrared converter vacuum tube which converts an infrared image incident upon a photo emissive surface responsive to infrared photons, to electrons which are accelerated by a high voltage and impinge on phosphor screen to thereby produce a greenish, florescent image of a target. This type of device required an infrared illuminator to illuminate a target.
Modern night vision riflescopes utilize more sophisticated infrared image devices, and/or image intensifiers which have a sufficiently high brightness amplification factor that minuscule levels of target illumination provided by starlight are sufficient to produce an image of a target, hence the name “starlight scope.”
Whatever imaging technology is utilized to obtain an image of a target in low light level conditions, the requirement for maintaining the line of sight of the imaging device stably aligned with the bore of the rifle on which the device is mounted remains. Accordingly, utilization of such devices requires that they be either semi-permanently mounted to a rifle, or removably mounted to the rifle in a manner which ensures that the device will be remounted to a precisely pre-determined, bore-sighted orientation relative to the rifle bore axis, each time it is replaced after removal. It should be noted that a typical night vision riflescope cannot be used during daylight conditions because the high light amplification of such devices results in overly bright, low contrast image under normal ambient lighting conditions. Also, some low-light level devices can be permanently damaged by normal levels of illumination.
For the foregoing reasons, it is generally necessary to provide a rifleman with separate daylight and night vision riflescopes, requiring the rifleman to substitute one for the other when shifting between nighttime and daytime tactical operations. Therefore, it would be highly desirable to provide a device which would enable night vision devices to be removably attached in precise coaxial alignment with a daylight riflescope which was semi-permanently mounted and accurately bore-sighted to a rifle, thus enabling the rifle to be used in both daytime and nighttime lighting conditions.
Brough et al, U.S. Pat. No. 6,449,419, discloses a clamping device for coaxial coupling two optical viewing devices, which has a pair of longitudinally spaced apart split collars, each of which has a bore diameter reducible into clamping engagement with the barrel of an optical device inserted into the bore, by means of a toggle clamp which releasably draws more closely together a pair of circumferentially spaced apart cylindrical ring segments. However, there remains a need for a clamping device for optically coupling a relatively long, heavy auxiliary optical device such as a night vision scope, to a riflescope, which includes means for preventing the long, unsupported moment arm of the device from causing deviation in optical alignment between the riflescope and optical accessary device, as a result of gravitational force acting on the unsupported device, and/or inertial torques exerted on the accessory device relative to the riflescope as a result of accelerating motions of a rifle during maneuvers. Also, it would be desirable to have a clamping device for maintaining an accessory optical device in precise coaxial alignment with a riflescope, and which would also enable the accessory device to be quickly and easily swung away from the riflescope to enable direct viewing through the riflescope, and swung back into a precise coaxial optical alignment with the riflescope, to enable coupled use of the devices.
The present invention was conceived of to provide such a device.